Detecting the micellization of anionic surfactants by a colorimetric and fluorescent probe based on electrostatic attraction

A novel fluorescent probe labeled with cation, N-n-alkyl-4-(1-methylpiperazine)-1,8-naphthalimide iodide ([C₈ndi]I), has been applied as a colorimetric and fluorometric probe for detecting the micellization of anionic surfactants. The critical micellization concentration (cmc) of anionic surfactants can be conveniently determined by the change on absorption and fluorescence spectra of [C₈ndi]I. The probe displays highly sensitive and selective spectroscopic responses accompanied with distinctive color change (from colorless to light green). These methods are proved to be reliable as the results are in accordance with those of the standard methods. Besides the advantage of visual detection, the multiple spectroscopic methods (absorption and fluorescence) by using [C₈ndi]I as probe are also simple and convenient. One can choose any spectroscopic parameter, such as position or intensity of the absorption and emission peaks, to monitor the micelle formation process of anionic surfactants.